The coating of substrates, particularly glass substrates that have optically effective layers, is wide spread. Examples include so-called low-E or thermal insulation layers for architectural glazing, antireflective layers such as for VDUs and the like. Such layers are deposited for example by sputtering techniques under vacuum conditions, it being preferable, for economic reasons, to use substrates which cover a large surface area.
In this regard, it is important that the quality of the deposited layers can be checked so as to ensure that the desired physical properties are obtained, particularly in a homogeneous manner, across the entire substrate surface area. Physical properties are defined here as, for example, the layer thickness, the transmittance or reflectance, the refractive index and the like.
The prior art, for instance, examines the uniform layer thickness of deposited layers in that once a substrate has been appropriately prepared beforehand and after the layer has been deposited, the substrate is measured mechanically, for example by means of a profilometer. For this purpose, large substrates, such as architectural glazing, will require, for example, 2,000 measuring points spread across the substrate, which, if the measurement is taken mechanically, will mean a considerable amount of time and effort that is not, in fact, practicable.